trace: trace to help anayze issue

get_memcg_count.stp

# usage : stap -g get_memcg_count.stp
# I only verified it on CentOS 7 (kernel-3.10) @yafang

# With it we can calculate how many offline memcgs.
# This script gets all memcgs, and /proc/cgroup gets online memcgs.
#
#     all memcgs = online memcgs + offline memcgs

%{

#include <linux/rcupdate.h>
#include <linux/cgroup.h>
#include <linux/memcontrol.h>


        /* The embedded c function must have a return value.
         * If it doesn't has an argument, we must use a specified void.
         */
        int get_memcg_count(void)
        {
                struct cgroup_subsys_state *tmp;
                int count = 1;
                int i;

                rcu_read_lock();
		            /* CSS_ID_MAX is 65535, 0 is unused */
                for (i = 1; i < 65536; i++) {
                        tmp = css_lookup(&mem_cgroup_subsys, i);
                        if (tmp)
                                count++;

                }
                rcu_read_unlock();

                return count;
        }

%}


function do_calc:long()
%{
        int count = 0;
        count = get_memcg_count();
        STAP_RETVALUE = count;
%}

probe begin {
        printf("probe begin\n");
        printf("count %ld\n", do_calc());
}

probe end {
        printf("probe end\n");
}